Substituent position engineering of diphenylquinoline-based Ir(iii) complexes for efficient orange and white PhOLEDs with high color stability/low efficiency roll-off using a solution-processed emission layer. Issue 1 (27th November 2015) - Sarada, Ganguri
Abstract : The location of –CF3 group on 2, 4-diphenylquinoline based Ir(iii ) complexes is key for attaining high performance in solution-processed PhOLEDs. Abstract : Three new heteroleptic Ir(iii ) complexes o -LIrpic, m -LIrpic, and p -LIrpic (L = CF3 DPQ) consisting of 2, 4-diphenylquinoline (DPQ) with a –CF3 group at ortho ( o )/ meta ( m )/ para ( p ) positions of the metalated phenyl ring, respectively, as the main ligands were synthesized and used as emitters in phosphorescent organic light-emitting diodes (PhOLEDs). We realized that –CF3 position extremely affects the crucial photophysical and electronic properties such as emission color, photoluminescence quantum yield (PLQY) and energy levels of these Ir(iii ) complexes resulting in –CF3 position-dependent performance of their PhOLEDs. To verify the effect of –CF3 group position on device performance, three other Ir(iii ) complexes o -LIrtmd, m -LIrtmd, and p -LIrtmd were synthesized using the same main ligands but a different ancillary ligand. In the two series of Ir(iii ) complexes, the devices with m -CF3 based complexes are outstanding in performance compared to o - or p -CF3 based ones due to the enhanced PLQY and well suppressed non-radiative deactivations by m -substitution. Finally, the single emission layer solution-processed orange and two-component white PhOLEDs fabricated using m -LIrpic as orange emitter achieved the maximum external quantum efficiency of 17.1% (43.9 cd A −1 ) and 21.1% (48.8 cd A −1 ), respectively, with highly stable color coordinates and low efficiency roll-off. This is the highest efficiency reported to date for solution-processed orange PhOLEDs using a small molecular host with easily accessible emitter.